Digital video can be delivered in either a broadcast mode, a switched mode, or in an on-demand mode. In broadcast mode, all channels are broadcasted from a source (e.g., a cable television system hub) to all the subscribers connected to that hub (e.g., a service group). Broadcast delivery broadcasts all channels all the time, even when a channel has no active viewers. As the number of channels being broadcast increases, bandwidth demands placed on the cable television system also increase. On-demand delivery occupies bandwidth only while the viewer demands the video, and is a type of unicast delivery (i.e., to a single destination) of video assets. Switched digital video offers improved bandwidth utilization by delivering channels with active viewers. Switched digital video (in a non-IPTV environment) can be either switched unicast or switched multicast (i.e., any subscriber can access the channel being broadcast and in that sense the video is delivered to multiple subscribers). Switched multicast provides the best bandwidth efficiency by not duplicating channels, while switched unicast offers the ability to personalize content and advertisement. Targeted advertisement in a switched video delivery can either be based on geographic/demographic zones or based on individual subscribers.
In a traditional (non-IPTV) switched digital environment (Motion Picture Experts Group (MPEG) video delivery), there are several major components: a switched digital video session manager; an edge quadrature amplitude modulator; a video source; and a set top box switched client. When a user selects a channel, the set top box switched client signals the switched digital video session manager of the selected channel and the service group the set top box belongs to. If the channel is already delivered to the service group, the switched digital video session manager simply returns the tuning information to the set top box switched client. Otherwise, the switched digital video session manager will instruct the edge quadrature amplitude modulator to deliver the selected channel to the service group. The edge quadrature amplitude modulator then joins the multicast video source and delivers the video to the service group.
Policy control may be added in the switched digital video session manager to facilitate selection of targeted content (e.g., targeted advertisement). Based on current bandwidth utilization of the service group, the switched digital video session manager decides if a zone based multicast version or a unicast version of a channel should be used. If a zone based multicast version is used, the switched digital video session manager instructs the edge quadrature amplitude modulator to join the multicast group assigned to that the channel. If a unicast version is used, the switched digital video session manager instructs the video source to deliver the unicast version to the edge quadrature amplitude modulator and the edge quadrature amplitude modulator will then deliver the channel to the set top box switched client.
In traditional (non-IPTV) MPEG transport stream video delivery, switched multicast provides the same copy of the stream to be shared among all viewers in a service group by associating a channel (e.g., Cable Network News (CNN)) to a frequency and program number pair. However, in switched unicast, multiple copies of the stream (e.g., CNN) would be transported over different frequency and program number pairs. Each subscriber is assigned a unique frequency and program number pair and tunes to a personalized copy of the stream (e.g., CNN).